Base member for electron discharge tubes



Feb. 21, 1950 G. N. PHELPs 2,498,378

BASE MEMBER FOR ELECTRON DISCHARGE TUBES Filed April 24, 1946 PatentedFeb. 21, 1950 BASE MEMBER FOR ELECTRON DISCHARGE TUBES George N. Phelps,Lancaster, Pa., assigner to Radio Corporation of America, aicorporationof Delaware Application April 24, 1946, Serial No. 664,466

3 Claims. 1

This invention relates generally to vacuum tubes and more particularlyto electron discharge tubes wherein the electrical leads from theelectrodes are sealed in the stein and also extend through the stem toserve as external base con tact pins.

In electron discharge tubes of this type, where the lead pins also serveas base contact pins, it has been found that there is frequent failurein the glasstometal seal of the tube stem caused by excessive orcontinuous strain being put upon the base pins during operation. In thistype of electron discharge tube, the breakage of this glass-to-metalseal between metal lead pins and the glass stem of the tube is usuallydue to a lateral bending of the base pins. This bending causes the oxidelayer of the pin to pull away from the glass or the metal to pull awayfrom the oxide layer. This lateral bending can be caused by severalfactors such as continuous socket strain or bending by bumping or sharpblows. Other causes of seal breakage can be due to misalignment of thetube socket. Furthermore, some types of tubes wherein the stem leadsform external base pins, also have a large and heavy envelope, such as acathode ray tube, for example. In such cases, the weight of the tube maybe supported by the tube socket directly and hence put considerablestrain on the glass-tometal seal in the tube stem.

Using heavier and shorter leads on such tubes does not solve theproblem. A more rigid pin would not have the required exibility and thuswould increase the danger ci seal breakage. Furthermore, it is alsodesirable in most tubes of the miniature or cathode ray type to keep thestem or neck of the tube as small as possible. Large and heavy leads intubes of these types would necessitate a crowding of the base pins andcut down desirable insulation between the leads. Also, it is expedientto keep down the cost of manufacture of these tubes by using pin sizeswhich conform to the apertures in standardized sockets.

It is an object of my invention, therefore, to

provide an improved vacuum tube which overcomes the disadvantages of theprior art. In particular, the object of my invention is providing meansto protect the glass-to metal seal around the stem leads so that shouldthe lead pins outside of the tube be bent and straightened suchtreatment would not endanger the seal. An additional object of thisinvention is to provide a protective cap for the exhaust tube after ithas been tipped 01T. A further object of the inven- 2 tion is providingan electrostatic shield for the base leads of the tube.

Accordingly, my invention involves a vacuum tube having a glass stemthrough which are sealed a plurality of lead pins in a circle concentricwith the center of the stem. The lead pins are of a type sufficientlyrigid to serve as external contact or base pins. Due to severalconditions as outlined above, for example, the glass-to-metal seal inthe stem between the load pins and the glass stem is frequently broken.I have minimized this danger of seal breakage, by utilizing aring-shaped plate of a plastic or similar insulating material. Aperturesare drilled or punched through the plate of a diameter of the size ofthe wire being used as the base pins of the tube. When the plate isiitted over the pins and xed tightly against the base of the tube, theglass-to-metal seal of the pins is protected against breakage. This isdue to the fact that the bending of each base pin will take place at thebottom surface Aof the plate and thus remove the strain of bending fromthe glass-tometal pin seal. A cup-like portion formed at the center ofthe plate may serve an an exhaust tube tip cover. This cup-like portioncan be filled with a basing cement and the plate and cup member togethercan be fitted in an abutment against the bottom of the tube stem withthe pins of the tube projecting through the apertures of the plate. Heatis then applied to bake out the cement and hold the base on the tube.The cup-like portion may also be made of a drawn metal part crimped orstaked into the plastic plate. Thus, the cuplike portion can provide, ifdesired, an electrostatic shield for the pins. If there is no exhausttube present, or if it is deemed unnecessary to cover it, a ring-shapedplate can be readily held in place mechanically by a slight crimping orstraining action on the pins just below the plate. A lug may also beadded to the cup-like portion to index the tube within its socket.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing, in which-Figure 1 is a detailed elevational view partly in vertical section of atube and base assembly according to the invention;

Figure 2 is an elevational view in perspective of the tube baseaccording to the invention;

Figure 3 is a bottom plan view of the tube base according to theinvention;

Figure 4 is a detailed elevational view partly in vertical section of atube and base assembly according to a modication of the invention; and

Figure is a detailed elevational view partly in vertical section of atube and base assembly according to the further modification of the in-Vention.

Referring to Figure 1 there is partly shown an electron discharge tubecomprising a glass envelope I enclosing an anode plate 2 and a cathodeelectrode 3. Enclosing the lower part of the envelope I is a glass stemor header portion 4 sealed at 6 to the envelope. Lead pins 8 are sealedwithin the glass header at I8, for example. These pins extend throughthe header 4 to form external base contact pins for the tube. Normally,the stem or header portion 4 is a flat circular button-shaped disc andin which the lead pins 8 are sealed in a circle concentric with thecenter of the button stem. The button stem 4 may also be provided withan exhaust tubulation tip 5 extending outwardly from the bottom of thestem portion 4. Thus, the envelope 2 can be exhausted through theexhaust tip 5.

' A base member I2 preferably of plastic is mounted on the bottom of thetube stem 4. This base member I2 includes a ring-shaped rigid plate I4fixed in abutment against the bottom of the tube stem or header 4. Inthe rigid plate I4 are formed apertures I6 positioned in a circle toconform with the arrangement of the base pins in the stem. The aperturesI6 are made to t the base pins 8 of the tube within a very smallclearance in the order of .003.004, for example. With this arrangement,the plate I4 will tightly grip the pins 8 at the point where they leavethe glass stem and thus provide a rigid support for the pins in thisregion immediately adjacent to the glass stem. With this plate structureI4 in place, tightly, against the bottom face of the stem 4, I havefound that frequent-lateral bending of the pins at any angle even untilwork hardening causes them to break will not excessively disturb theglass-to-metal seal at I0. I'have found that this is due to the factthat the point of bending of the pin is at the edge of the bottomsurface of plate I4. That is, the bending point of the pin is moved awayfrom the glass seal in the glass header or stem 4 a distance equal tothe thickness of plate I4. The glass-to-metal seal in the stem is ableto withstand any strain that may develope in a direction longitudinallyof the lead pins 8 during bending of the pins.

In Figure l, a cup-like portion I8 is formed integral with the plate I4.This portion I8 is so constructed as to iit over the exhaust tubulationtip 5 and provides a protective cap for the tubulation. Furthermore, 4aprojecting rib 20 may be formed on the cup I8 to index the tube withinits socket as is well known in the art.

'A preferred method for attaching the base member I2 to the bottom ofheader `4 of the vacuum tube is to fill the cup-like portion I8 with abasing cement I9 and place the base member against' the stem portion 4of the tube, so that the lead pins 8 pass through the apertures in theplate I4 and the exhaust tabulation ts into cup portion I8. Heat is thenapplied to bake out the cement, thus rmly xing plate portion I4 inabutment against the bottom of the glass header or stem 4 of the tube.-

4 Often, it is desirable to electrostatically shield the electrode partsof a discharge tube from each other. To complete the shielding effect inthe region of the base pins of the tube, I propose 5 to modify myinvention as disclosed in Figure 4. This modification includes a rigidring-shaped plate 22 corresponding to plate I4 of Figure l.

A cup-like portion 24 is formed of metal to act as an electrostaticshield between the several lead pins 8. This cup portion 24 is attachedat its upper end to the inside edge 23 of plate 22 by means such ascrimping 25 and 26. To effect the necessary electrostatic shielding, thecup is grounded, preferably by an electrical connection to theparticular pin 8, which, during operation of the tube, is connected toground or some suitable base potential. Cup 24 may be used as aprotective cap for tubulation 5 and may also be provided with anindexing rib 20 similar to the same features of Figure 1. The tube baseI2 shown in Figure 4 may also be cemented to the exhaust tubulation 5 inorder to firmly fix plate 22 in abutment to the tube stem.

Some types of discharge tubes do not have an exhaust tubulation in thetube stem. In such cases, the method of cementing the tube base I2 tothe bottom of the vacuum tube cannot be used, I have provided othermounting means for locking the rigid plate to the bottom of the stemportion 4. In Figure 5, I disclose a type of base member I2 with a rigidplastic plate 22 and a metal shield cup 24 similar to that which isillustrated in Figure 4. I propose to lock plate 22 directly to the leadpins 8. The preferred fastening means disclosed in this Figure 5comprise a crimped or flattened portion 28. On each lead pin 8 thiscrimped or flattened portion 28 is placed just below the plastic plate22 in such a way that the plate is held tightly under pressure againstthe tube stem 4. In this modication cup portion 24 may be either ofplastic material formed integral with the plate as shown in Figure 1, ora separate metal cup as described in Figures 4 and 5. Whatever the typeof cup portion used in the base members shown in Figures 1 to 5inclusively, an indexing rig 20 may be formed within the cup to properlyposition the tube in its socket.

Portion I8 in Figures 1 to 3 and portion 24 in Figures 4 and 5 have beendisclosed as a cuplike structure. However, it is evident that thiscup-like portion may take any desired form such as an open cylinder vora simple plate structure in order to provide an electrostatic shield. Ifthe shielding effect of the base member I2 is not necessary or desired,portion I8 or portion 24 may be dispensed with. In this case the rigidplate member may be fixed directly to the tube by means shown in Figure5, for example.

While certain specific embodiments have been illustrated and described,it will be understood that various changes and modiiications may be madetherein without departing from the spirit and scope of the invention.

What I claim is:

1. An electron discharge tube including a stem portion, a base membercomprising a plate structure and a metal cup attached thereto, meansfixing said plate structure in abutment against 70 said stem portion, aplurality of lead pins sealed in said stem portion and extending throughsaid plate and terminating beyond said plate in adjacent relationshipwith said cup, a portion of said cup positioned between two of said lead75 pins to provide electrostatic shielding therefor,

5 said plate structure tightly embracing said lead pins intermediate theends thereof.

2. An electron discharge tube including an envelope comprising aflattened stem portion closing one end thereof and an exhaust tubulationprojecting outwardly from said flattened portion, a base member fixed tosaid flattened portion and including a cup portion enclosing saidtubulation and a plate structure having a surface abutting said attenedstem portion, a plurality of lead pins sealed through said flattenedstein portion and extending through said plate at the abutting surfacethereof, said lead pins terminating beyond said plate, said platetightly gripping said lead pins intermediate the ends thereof.

3. A base member, for an electron discharge tube having a plurality oflead pins sealed in the stem of the tube, comprising a. plastic ring- 6shaped plate structure, said plate structure having aperturestherethrough to t over said base pins and tightly grip said pinsintermediate their ends when said plate structure is mounted in abutmentagainst the stem or" the tube, a metal cup fastened to said platestructure for eleetrostatically shielding said pins.

GEORG-E N. PHELPS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,131,923 Thomas Oct. 4, 19382,192,760 Thorson Mar. 5, 1940 2,337,401 Miller Dec. 21, 1943 2,424,990Krim Aug. 5, 1947

